The benefits that may be realized when aircraft are moved during ground travel without operation of an aircraft's main engines are gaining wider recognition in the airline and related industries. Proposals for independently moving aircraft on ground surfaces were initially made decades ago, and various structures and methods useful to independently drive aircraft on the ground without operating engines or assistance from tow vehicles have been proposed since then. Until recently, however, systems and methods for achieving the autonomous ground travel of aircraft have not been successfully implemented.
One system proposed for moving aircraft autonomously during ground travel that has been successfully demonstrated to drive an aircraft in a desired direction at a desired taxi speed without operation of the aircraft's main engines or assistance from an external tow vehicle is mounted to drive one or more nose landing gear wheels or main landing gear wheels so that the wheel or wheels operate as self-propelled drive wheels. Such a system is described, for example, in commonly owned U.S. Pat. No. 7,975,960 to Cox et al; U.S. Pat. No. 8,220,740 to Cox et al; and U.S. Pat. No. 8,240,599 to Edelson et al. A non-engine drive means that is controllable to drive a landing gear wheel may be mounted within or adjacent to the wheel and may be controlled, preferably by an aircraft pilot, to drive the wheel at a desired torque and/or speed required to move the aircraft on a ground surface. While a preferred non-engine drive means in such a system is one or more electric motors, preferably powered by the aircraft's auxiliary power unit, the drive system may also be powered by hydraulic or pneumatic drive motors.
Another system proposed for moving aircraft on the ground without using the aircraft's engines is designed to be mounted on and drive aircraft wheels with brakes, typically only an aircraft's main landing gear wheels. This system is described in U.S. Pat. No. 8,360,360 to Cros et al and U.S. Pat. No. 8,528,856 to Charles et al. The Cros et al system may use a hydraulic or electric drive motor. The Charles et al system relies on an electric motor to move the aircraft during taxi and includes additional structure to cool aircraft brakes during taxi. Charles et al notes, moreover, that some modification of the aircraft's landing gear doors may be needed to accommodate the disclosed system.
The aircraft autonomous drive systems or taxi systems described above are specifically designed to be mounted on and in connection with aircraft landing gear wheels and/or other landing gear structures and are effectively part of the aircraft's landing gear. Consequently, care must be taken so that these drive or taxi systems avoid interference with landing gear operation. Such drive or taxi systems, when mounted on an aircraft's main landing gear, should also not negatively impact aircraft brake capacity. Since the drive and taxi systems currently proposed may be mounted within landing gear wheels, these systems are exposed to many of the same stresses to which other landing gear structures are exposed, including shocks accompanying landing of an aircraft, high rotational velocities and acceleration speeds, and a range of temperature variations. Additionally, the weight of motors and other drive system elements may increase strains and stresses on landing gear components during landing gear operation, and drive system design for autonomous aircraft taxi must take these and the aforementioned factors into account.
There is a need, therefore, for a drive or taxi system capable of driving an aircraft autonomously without reliance on operation of the aircraft's engines or external vehicles during ground travel that is designed to avoid interference with operation of landing gear components or landing gear wheel brakes and that is not subjected to shocks and stresses or other potentially adverse events produced by a landing aircraft. There is a further need for such a drive or taxi system that does not increase potential adverse effects on aircraft landing gear during operation.